Beam modeling and VMAT performance with the Agility 160-leaf multileaf collimator.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• The Agility multileaf collimator (MLC) offers advanced features for radiotherapy.
• Volumetric-modulated arc therapy (VMAT) requires precise beam delivery.
• Accurate modeling of MLCs in treatment planning systems is crucial for VMAT.

Purpose of the Study:

• To create and validate a Pinnacle3 treatment planning system beam model for the Agility MLC.
• To evaluate the performance of the Agility MLC in delivering VMAT treatments.
• To compare Agility MLC VMAT delivery times and accuracy against an MLCi unit.

Main Methods:

• Developed a 6 MV beam model for the Agility MLC in Pinnacle3.
• Verified the beam model using dose measurements under irregular fields.
• Created and delivered VMAT treatment plans for head-and-neck patients using Agility MLC with and without continuously variable dose rate (CVDR), comparing to an MLCi unit.

Main Results:

• The Agility MLC beam model demonstrated high accuracy, with interleaf leakage of 0.2% and mean dose agreement of 1.3% for irregular fields.
• Agility VMAT plans achieved equivalent quality and accuracy to MLCi, with 95% of measurements within 3% and 3 mm.
• Mean delivery times were significantly reduced: 133s (Agility with CVDR), 171s (Agility without CVDR), vs. 282s (MLCi).

Conclusions:

• Pinnacle3 accurately models the Agility MLC.
• Agility MLC facilitates accurate VMAT plan delivery.
• The Agility MLC significantly reduces VMAT treatment delivery time compared to MLCi.